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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Please, explain the Number part. How does regexp reveal the prime number?
About string one. It's not because of 'y', it's about capital 'O' in the string. Regexp really don't need the
iflag here.